Selective Catalytic Reduction Applications Research Articles

Enhancement of SCR denitrification control strategy considering fluegas temperature fluctuation: Fundamental principle and performance evaluation

Nitrogen oxides (NOx) constitute a primary pollutant in coal-fired power plants, and are mitigated through the application of selective catalytic reduction (SCR). Coal-fired power plants should frequently change their output power to help the power grid to accommodate high penetration of intermittent renewable power. However, NOx emission transient overshoot often occurs in coal-fired power plants when coal-fired power plants dynamically change their output power. To address this issue, dynamic models for both coal-fired power plants and SCR denitrification were established. The study identifies fluctuations in fluegas temperature as a critical factor contributing to transient NOx overshoots. The change law of SCR reaction temperature during load cycling processes is obtained, and its prediction model based on neural network algorithm is developed. An enhanced control strategy, accounting for the temperature variations at the SCR inlet, was subsequently introduced. Performance comparisons indicate that the enhanced control strategy effectively eliminates transient NOx overshoots during load cycling processes. Specifically, the maximum NOx emissions during loading down and loading up processes under the enhanced control strategy are 48.62 and 49.44 mg m−3, representing reductions of 7.36 and 4.63 mg m−3 compared to the original control strategy. Additionally, when the enhanced control strategy is adopted, the cumulative ammonia (NH3) consumption decreases by 0.48 and 11.84 g m−3 during loading down and loading up processes, respectively.

Design and evaluation of novel static mixers for SCR application

Static mixers are widely used in selective catalytic reduction (SCR) systems to improve the conversion efficiency and service life of the catalyst by better mixing ammonia and the exhaust stream. However, the structure of the mixer needs to be designed carefully to minimise the loss of the system pressure caused by its installation. In this work, experiments and simulations are conducted to evaluate the mixing performance of the static mixers and the system pressure loss. The simulations and experimental results have good agreement. Four novel static mixers are designed and compared with a commercial static mixer to demonstrate their performance. The results show that the box mixer can accomplish less pressure loss (690 Pa) and more homogenous mixing (CoV = 5.4%), and it can thus be used to improve the mixing of ammonia and the exhaust stream in SCR systems.

Exhaust gas aftertreatment to minimize NOX emissions from hydrogen-fueled internal combustion engines

Hydrogen-fueled internal combustion engines are a promising CO2-free and zero-impact emission alternative to battery or fuel cell electric powertrains. Advantages include long service life, robustness against fuel impurities and a strong infrastructural base with existing production lines and workshop stations. In order to make hydrogen engines harmless in terms of pollutant emissions as well, NOX emissions at the tailpipe must be reduced as low as the zero-impact emission level. Here, the application of selective catalytic reduction (SCR) catalysts is a promising solution that can be rapidly adopted from conventional diesel engines.This paper therefore investigates the influences of the hydrogen concentration in the raw exhaust gas, of the NO2/NOX ratio and of the space velocity on the performance of two different SCR technologies. The results show that both types of SCR, copper-zeolite and vanadium-based, have their advantages and drawbacks. Copper-based SCR catalysts have an early light-off temperature and reach maximum efficiencies of up to >99%. On the other hand, vanadium systems promise almost no secondary N2O emissions. As a result, we combined both approaches to create a superior solution with high efficiency and lowest secondary emissions.

Alkali-resistant NOx reduction over FeVO4/TiO2 catalysts via regulating the electron transfer between Fe and V

The presence of alkali metals in exhaust gas from stationary resources causes a grand challenge for the practical application of selective catalytic reduction (SCR) of NOx with NH3. Here, alkali-resistant NOx reduction has been successfully implemented via tailoring the electron transfer over Fe and V species on FeVO4/TiO2 catalysts. The strong interaction between Fe and V induced electron transfer from V to Fe and strengthened the adsorption and activation of NH3 and NO over active VOx sites. In the presence of K2O, the strong electron withdrawing effect of Fe offset the electron donating effect of K on the VOx species, thus protecting the active species VOx to maintain the NOx reduction ability. The enhanced adsorption and activation of NH3 allowed SCR reaction to proceed via E-R mechanism even after K2O poisoning. This work elucidated the electronic effects on the alkali metals resistance of traditional ferric vanadate SCR catalysts and provided a promising strategy to design SCR catalysts with superior alkali resistance.

Superior PbO-resistance of CeO2/ZrO2 catalyst promoted by solid superacid SO42−/ZrO2 for selective catalytic reduction of NOx with NH3

The serious deactivation of denitration catalysts caused by heavy metals still a thorny issue in the practical application of selective catalytic reduction of NOx with NH3. Herein, we proposed a novel anti-poisoning strategy by designing SO42−/ZrO2 superacid supported CeO2/ZrO2 catalyst, and the effect of SO42−/ZrO2 supported CeO2/ZrO2 for PbO-resistance NOx catalytic reduction was investigated. It was worthy to note that the introduction of solid superacid SO42−/ZrO2 significantly enhanced catalytic performance over the entire temperature range, with an exceptionally high NOx removal efficiency over 98 % during 250–500 °C. When 2 wt% PbO was deposited on the fresh catalyst, the catalytic activity of CeO2/ZrO2 catalyst decreased obviously, while CeO2/ZrO2-S catalyst can still maintain a higher NOx conversion over 90 % from 275 to 500 °C. The characterization results confirmed that the introduction of solid superacid SO42−/ZrO2 enhanced the surface acidity and promoted the transformation from Ce4+ to Ce3+. The results of in situ DRIFTS implied that the Eley-Rideal (E-R) mechanism was obeyed over CeO2/ZrO2 catalyst, and both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms were followed over CeO2/ZrO2-S catalyst in the SCR process. With regard to poisoned catalysts, the NH3 adsorption was inhibited to some extent, while the reaction mechanism wasn’t changed by PbO poisoning.

Reduction of emissions with cow urine as a catalyst in SCR system using response surface methodology

Nitrogen oxides are the most dangerous contaminants to human health and the atmosphere. The goal of this research work is to establish a feasible and promising approach for reducing NOx emissions from the exhaust pollutants of a diesel engine without any addition in fuel and impact onother pollutant emissions with cow urine as a catalyst. The experiments were conducted using a modified selective catalytic reduction application mounted on a single-cylinder diesel engine for water-based diesel exhaust with concentrations of 250, 500 and 750 ml at speeds of 800, 1600, and 2400 rpm for each sample. The response parameters such as NOx, CO, HC, CO2, smoke capacity, specific fuel consumption, and brake thermal efficiency were predicted employing the response surface method. Consequently, the maximum reduction of NOx was found to be 73.67% for cow urine having a concentration of 750 ml with 250 ml water tested under the speed of 800 rpm.

Investigation of cross-stream spray injection and wall impingement in a circular channel for SCR application

A parametric study of cross-stream pulsed spray injection and wall impingement characteristics in a circular channel has been carried out with an objective to investigate performance improvement in selective catalytic reduction (SCR) systems for exhaust gas after-treatment in diesel engines. The spray computations are performed based on a combined Eulerian and Lagrangian based modeling approach for the continuous and the discrete phases respectively. The simulation results are validated using the in-house experimental data for water injection in both open atmospheric and channel flow conditions. The spray structure, penetration, and droplet size are compared and good agreement between the experiments and simulations is demonstrated. Though the focus of the present work is on studying the influence of liquid preheating on post-impingement spray and wall-film characteristics as well as evolution of species mass fraction, the effect of air mass flow rates, and temperature, and the choice of the working liquid (water or Urea Water Solution (UWS)) are also investigated. While the mass flow rate of air and the selection of the above liquids for spray injection are found to have marginal influence on the results, the liquid preheating is shown to strongly affect the droplet evaporation and thus, the spray impact process. Especially, the liquid injection temperature that leads to flash evaporation results in reduced wall filming, higher ammonia generation rate and spatial uniformity of NH 3 across the channel. This paper demonstrates preheating as a promising approach for the improvement of SCR performance. • Spray injection and wall impingement in a duct air flow relevant to SCR systems is numerically investigated. • The predicted post-impingement droplet size and spatial distribution compared well against the in-house experiments. • Marginal influence of air mass flow rate and choice of the liquid (water or UWS) is observed. • Preheating the injected liquid is a viable alternate for performance optimization of the SCR systems. • Especially, the flash evaporation condition ensures reduced wall filming and, higher rate of NH 3 and its spatial uniformity.

Revealing M (M = Cu, Co and Zr) oxides doping effects on anti-PbCl2 poisoning over Mn-Ce/AC catalysts in low-temperature NH3-SCR reaction

Lead salts poisoning was a great challenge for the catalysts application in selective catalytic reduction (SCR) reaction of NOx with NH3 in stationary sources. Herein, several typical transition metal (Cu, Co and Zr) oxides modified Mn-Ce/AC catalysts were prepared by impregnation method, and the effects of Cu, Co and Zr doping on resistance PbCl2 poisoning for the catalyst were investigated. The addition of three transition metal oxides improved the PbCl2 resistance of Mn-Ce/AC catalyst and maintained excellent low-temperature denitrification activity of the catalyst. The lead resistance performance of the three metal oxides followed: Cu > Co > Zr oxides. The NO conversion of Cu-doping catalyst after PbCl2 poisoning was only ca. 10% lower than that of fresh Mn-Ce/AC catalyst at 225 °C. Cu, Co and Zr doping could decrease the loss of specific surface area caused by poisoning, while Cu-doped catalyst showed lowest crystallinity of active components. Meanwhile, the contents of Mn4+ and chemisorbed oxygen in Cu-doped catalyst were higher than those in Co- or Zr-doped catalysts. Cu, Co and Zr doping improved the surface acidity and redox performance of the poisoned catalysts, with Cu-doped poisoned catalyst exhibiting nearly the same surface acidity and redox performance as the fresh Mn-Ce/AC catalyst. Furthermore, Cu doping could also improve NO adsorption and was in favor to the SCR process. Besides, in situ DRIFTS results showed that the catalytic reaction pathways of all the poisoned or modified catalysts were in accordance with both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. Finally, a possible anti-PbCl2 poisoning mechanistic model of (Cu, Co and Zr) oxides modified on Mn-Ce/AC catalyst was proposed.

Enhancement of Surface Area of Cordierite Structure by Oxalic Acid Treatment for SCR Applications

Cordierite (2Al2O3-5SiO2-2MgO) is the main carrier structure that enables the positioning of catalytic nanoparticles on the exhaust pipe in the selective catalytic reduction (SCR) applications. In order to be loaded more catalytic nanoparticles into this structure, it must be modified by acid treatment. In our study, these structures were treated with the different oxalic acid ratios for 2 and 4 hours. Brunauer, Emmet and Teller (BET) analysis were employed to measure the surface areas of acid-treated cordierite structures and scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) analysis was used to examine morphological structures of them. In consideration of BET analysis result, the surface area measurements of these structures reached up to 163.601 m2/g. The obtained value was about 327 times greater than the surface area of no treatment cordierite. In result of the SEM analysis, while the percentage of aluminum (Al) and magnesium (Mg) elements on the surface of these structures decreased, that of silicon (Si) increased. The reason of the high surface area is the formation of the pure amorphous silica due to the removal of Al and Mg ions from the surface of the cordierite. Thus, further coating of the catalytic nanoparticles on the cordierite surface could be allowed. As a result of this study, it could be said that the acid amount of the solution and the acid treatment duration enhances the surface area of the cordierite.

Self-Defense Effects of Ti-Modified Attapulgite for Alkali-Resistant NOx Catalytic Reduction.

Nowadays, the serious deactivation of deNOx catalysts caused by alkali metal poisoning was still a huge bottleneck in the practical application of selective catalytic reduction of NOx with NH3. Herein, alkali-resistant NOx catalytic reduction over metal oxide catalysts using Ti-modified attapulgite (ATP) as supports has been originally demonstrated. The self-defense effects of Ti-modified ATP for alkali-resistant NOx catalytic reduction have been clarified. Ti-modified ATP with self-defense ability was obtained by removing alkaline metal cation impurities in the natural ATP materials without destroying its initial layered-chain structure through the ion-exchange procedure, accompanied with an obvious enrichment of Brønsted acid and Lewis acid sites. The self-defense effects embodied that both ion-exchanged Ti octahedral centers and abundant Si-OH sites in the Ti-ion-exchange-modified ATP could effectively anchor alkali metals via coordinate bonding or ion-exchange process, which induced alkali metals to be immobilized by the Ti-ion-exchange-modified ATP carrier rather than impair active species. Under this special protection of self-defense effects, Ti-ion-exchange-modified ATP supported catalysts still retained plentiful acidic sites and superior redox ability even after alkali metal poisoning, giving rise to the maintenance of sufficient NHx and NOx adsorption and the subsequent efficient reaction, which in turn resulted in high NOx catalytic reduction capacity of the catalyst. The strategy provided new inspiration for the development of novel and efficient selective catalytic reduction of NOx with NH3 (NH3-SCR) catalysts with high alkali resistance.

Sulfur/water resistance and regeneration of MnOx-CeO2/TiO2 catalyst for low-temperature selective catalytic reduction of NOx

Mn-based catalysts present a great prospect for application in selective catalytic reduction (SCR) of NOx with NH3 at low temperatures, due to their high low-temperature catalytic activity. However, poor resistance of Mn-based catalysts to SO2 and H2O restricts their industrial application. This paper investigates the SO2&H2O resistance of MnOx-CeO2/TiO2 catalyst and discusses the poisoning mechanism based on catalytic characterizations. The results indicate that MnOx-CeO2/TiO2 catalyst exhibit high tolerance to SO2 poisoning mainly because the surface sulfates are preferentially formed on Ce dopants so that protect the main active component (MnOx). Catalytic deactivation become more severe when SO2&H2O are simultaneously present, which implies that SO2&H2O exhibit a synergistic toxicity in poisoning catalyst. Interestingly, the presence of H2O can alleviate the formation of surface metal sulfates on catalyst to some extent, for the surface reactive oxygen species and the surface acid sites are preserved to fulfill the low temperature SCR reaction cycle. Thermal regenerations under different atmosphere (e.g., O2 and H2O) are conducted for the SO2 poisoned catalyst. Effective regeneration of the sulfated catalyst can be realized and their regeneration mechanisms are explored by utilization of several catalytic characterizations.

Experimental and Numerical Analysis of an Innovative Mixer Geometry for Urea Injection in SCR Applications

Selective catalytic reduction (SCR), based on the injection of urea-water-solution (UWS), is one of the prevailing and more effective approaches to reduce NOx emissions in diesel engines. To improve the performance and durability of the system, it is crucial to develop reliable simulation tools able to correctly describe not only the urea conversion into ammonia and the mixing with exhaust gases but also the possible formation of solid deposits along with the engine’s exhaust line.In the present paper, two different exhaust systems for off-road applications are analyzed, both of them consisting of a diesel oxidation catalyst (DOC) followed by a diesel particulate filter (DPF), a UWS injection and a mixing device, and an SCR catalyst. Two alternative UWS mixing subsystems are evaluated, including a newly developed design. A 3D-CFD numerical analysis is carried out to assess the performance of both systems in terms of pressure drop, UWS spray, and liquid film development, in addition to flow velocities and species concentration uniformities at SCR catalyst inlet. A detailed analysis of droplet impingement on walls and liquid film development is enabled, thanks to a conjugate heat transfer (CHT) approach. Moreover, a deposit risk index is used to identify the areas of the systems where urea deposit formation is expected.Eventually, numerical results are compared with experiments on one operating condition chosen as the most challenging in terms of exhaust temperature and flow rate, both in terms of systems NOx conversion efficiency and deposit formation, showing a satisfactory agreement, thus paving the way to use the proposed synergetic numerical and experimental approach to further optimize the design and the system’s performance.

Green and Moderate Activation of Coal Fly Ash and Its Application in Selective Catalytic Reduction of NO with NH3.

Coal fly ash (CFA) is an ideal source for the preparation of heterogeneous catalysts due to its abundant silicon and aluminum oxides, but its activity needs to be improved. In this study, a green and moderate approach for CFA activation was proposed, and a series of CFA-based catalysts were prepared for NO selective catalytic reduction (SCR). The results indicated that CFA could be well activated via mechanochemical activation with 3 h of milling duration in 1 mol/L of acetic acid, and 90% of NO removal was achieved over the CFA-based catalyst in 250 to 375 °C. Two activating mechanisms, i.e., the enhanced CFA fragmentation and the motivated Al dissolution, were revealed during the mechanochemical activation. The former facilitated the formation of mesopores and the exposure of Fe components in CFA fragments, which enhanced the capacity of oxygen storage over the as-activated catalyst. The latter motivated the formation of Si-OH groups, which promoted the migration of electrons and the dispersion of V species, thereby increasing the capacity of NH3 adsorption over the as-obtained catalyst. Therefore, the performance of NO reduction was improved. The proposed activating approach could be a promising integration for CFA disposal and NO removal from inside coal-fired power plants.

Electrothermal alloy embedded V2O5-WO3/TiO2 catalyst for NH3-SCR with promising wide operating temperature window

Vanadia-based catalysts are widely used in selective catalytic reduction (SCR) reaction for reducing nitrogen oxides emissions, however, they only exhibit sufficient DeNOx efficiency within a narrow temperature window. In this study, a catalyst embedded with electrothermal alloy was prepared. The catalyst surface temperature could be heated using the electrothermal alloy, in order to widen the operating temperature window of the V2O5-WO3/TiO2 catalyst. Experimental results revealed that the electrothermal alloy embedded V2O5-WO3/TiO2 catalyst can maintain superior NH3-SCR performance and high resistance to H2O in a wide gas temperature range of 100–400 °C by controlling the surface temperature. In the meantime, the NH4HSO4 poisoned catalyst could be efficiently regenerated through electric heating, and NOx conversion can be restored to the level of fresh samples. Additionally, the effect of additives including methylcellulose and glass fiber, on the physicochemical properties of the plate-type catalyst was also investigated, and the catalyst samples were characterized by means of BET, XRD, NH3-TPD, H2-TPR, TG and SEM-EDS. This study proves the electric heating strategy is a promising way to enhance the performance of the V2O5-WO3/TiO2 during wide temperature SCR applications.

Solid Selective Catalytic Reduction: A Promising Approach towards Reduction of NOx Emission from Exhaust of CI Engines

The rising rate of pollution in urban areas has become a worldwide concern in recent years. Diesel engines are considered one of the largest contributors to environmental pollution caused by exhaust emissions, and they are responsible for several health problems as well. Diesel engines contain carbon monoxide, carbon dioxide, unburned hydrocarbons, and oxides of nitrogen. The reduction of Nitric oxides (NOx) emission from diesel engine exhaust is currently being researched by automotive manufacturers. After much research, selective catalytic reduction (SCR) technology was discovered to be effective in reducing nitrogen oxide emission from diesel engine exhaust. This paper is an attempt to explore the problems associated with the use of selective catalytic reduction (SCR) and compares selective catalytic reduction (SCR) with the latest technology named solid selective catalytic reduction (SSCR) for efficient reduction of NOx emission from the exhaust of diesel engines. The issue of contamination, malfunctioning, and freezing of diesel exhaust fluid (DEF) at low temperatures are the major problems associated with the application of SCR. It is observed that by controlling the quantity of ammonia slip, SSCR can give better performance in the reduction of NOx emission from the exhaust of diesel engines.

Active centers response to SO2 and H2O poisoning over Fe-W-Ni exchanged zeolite for high-temperature NH3-SCR: Experimental and DFT studies

Catalyst deactivation due to SO2 and H2O poisoning posed a grand challenge to the general application of selective catalytic reduction (SCR) of NOx with NH3 over metal-exchanged zeolites. In this work, we reported the activities of the synthesized Fe-Ni–W exchanged zeolite (0.5FNW-H) and pristine HZSM-5 were adversely affected by SO2 and/or H2O in the order of SO2 + H2O > H2O ≫ SO2 at high temperature (T > 500 °C). With the in-situ DRIFTs and in-situ UV–Vis analyses, the chelating bidentate HSO4-/SO42- was found to accumulate mainly on the framework Brønsted sites for HZSM-5, while on the Fe sites for the 0.5FNW-H, which caused the decline in the catalyst activities. Density functional theory study revealed that the dissociated hydroxyl from H2O facilitates the formation of sulfur complexes via bonding with the exchanged metal (ZFe-OH) and framework Brønsted sites (ZAl-OH) on the 0.5FNW-H and pristine HZSM-5, respectively. On the pristine HZSM-5, the dealumination of the tetrahedral coordinated Al (Ⅳ) atoms in zeolite lattice by H2O was identified by the 27Al solid-state NMR, which caused the irreversible loss of SCR functionality of HZSM-5. On 0.5FNW-H however, a much higher activation barrier for Al extraction from its neighboring metal site was observed, indicating the exchanged metal sites suppressed the bonding of –OH and Al atom in the framework and thus inhibiting the irreversible deactivation of HZSM-5. The findings are expected to provide rational guidance for the development of effective zeolite catalysts with high stability by regulating exchanged metal sites and framework Al.

Low-medium temperature application of selective catalytic reduction denitration in cement flue gas through a pilot plant

Low-medium temperature application of selective catalytic reduction (SCR) denitration in cement flue gas was established and investigated in this study. The 2000 h continuous operation shows the concentration of NOx at the outlet can be maintained at 24 mg/Nm3 on average, while due to the increase of SO2 in flue gas, the NOx concentration increased to 57.5 mg/Nm3 after long time operation. The sulfur deposition is the main reason for catalyst deactivation, and SO2 is still a big obstacle for low-medium temperature SCR application in cement flue gas. The denitration efficiency was tested as fluctuated from 73.5% to 86.2%, and ammonia concentration after SCR was as still as high as 22.5–60.0 mg/Nm3 due to the excessive ammonia injection from selective non-catalytic reduction (SNCR), shows serious ammonia escape problem for SNCR, and the potential application of hybrid SNCR-SCR technology. In order to maintain the denitration efficiency above 85.0%, the gaseous hourly space velocity (GHSV) should not be exceeded 2800 h−1, the electrostatic precipitators (ESP) setting at 60 kV was relatively appropriate, the temperature of the flue gas should be kept at above 200 °C. The concentrations and toxic equivalent quantities (TEQs) of the PCDD/Fs congeners in the flue gas raised greatly after SCR reactor, indicating the PCDD/Fs concentration should be concerned during the application of low-medium temperature SCR, especially for the waste co-disposal processes.

Insight into the effect of carrier on N2O formation over MnO2/MOx (M = Al, Si and Ti) catalysts for selective catalytic reduction (SCR) of NOx with NH3

The problems of easily inactivated by SO2 poisoning and high N2O formation for MnOx based catalysts hinder its application in selective catalytic reduction (SCR) of NOx with NH3. The SO2 poisoning mechanism has been well demonstrated, but the N2O formation mechanism was still controversial due to previous limited study. Herein, MnO2 supported on MOx (Mn/M, M = Al, Si and Ti) were prepared by wet impregnation method to investigate the carrier effect on the formation of N2O. Although all of selected supports had a large amount of surface acid sites, only forming strong active-support interaction can separate the activation sites of NH3 and NO + O2. Accordingly, the activation of NH3 and NO + O2 on MnTi was respectively occurred on TiO2 and MnO2, but both NH3 and NO + O2 was activated on MnO2 over MnAl and MnSi samples. The over-activation (NH2 dissociated into NH) of NH3 would be effectively inhibited when NH3 activation was occurred on TiO2, thus it can significantly suppress the formation of N2O. In contrast, the NH3 species would sharply decompose into NH on MnO2 and then lead to the high amount of N2O. Finally, we proposed some methods that might effectively improve the selectivity of MnOx-based catalysts.

Synthesis of SSZ-13 Zeolite in the Presence of N,N,N-Dimethylethylcyclohexyl Ammonium for Selective Catalytic Reduction of NOx

Abstract: Since NOx emission requirements from stationary and mobile sources are more strictly regulated in the United States, Europe, and other countries; researchers have conducted many studies to improve the performance of selective catalytic reduction (SCR) catalysts to meet more and more stringent emission standards. Herein, we reported the synthesis of small pore zeolite (Cu)-SSZ-13 using N,N,N-dimethylethylcyclohexylammonium as the structure directing agent. The catalytic activity of the fresh and hydrothermal aged copper exchanged supported on SSZ-13 catalyst was investigated in the SCR of NOx using NH3 as a reductant. Cu-SSZ-13 possessing a high SCR performance (NOx conversion reached approximately 100% at 250oC), and high hydrothermal stability in combination with an easy synthesis route is considered to be a potential catalyst for SCR application.
 Keywords: Zeolite, SSZ-13, synthesis, SCR, NOx.

Design of assembled composite of Mn3O4@Graphitic carbon porous nano-dandelions: A catalyst for Low–temperature selective catalytic reduction of NOx with remarkable SO2 resistance

The biggest challenge for selective catalytic reduction (SCR) of NO by NH3 at low temperatures is to develop robust catalysts with high resistance to SO2. Mn-based catalysts have attracted great attention for their excellent activity, but the poor SO2 resistance limits their application. Herein, we report a novel assembled composite featuring Mn3O4 nanoparticles embedded in defect-abundant graphitic carbon frame (Mn3O4@G-A) via a confinement–pyrolysis–oxidation strategy derived from MOF. The Mn3O4@G-A exhibits excellent activity (reaching over 90 % NO conversion in 100, 000 h−1 GHSV at 160 °C) and significantly improved SO2 resistance in comparison to pristine Mn3O4, and all the performance tests were conducted with 5.6 vol.% water vapor. By combining synchrotron radiation-based X-ray absorption spectroscopy and density functional theory calculation, we further discovered the positive role and the origin of graphitic carbon for improving SO2 resistance. Over the Mn3O4@G-A sample, the electrons can be transferred from graphitic carbon to Mn3O4 nanoparticles, which can regulate the electronic properties and oxidizing ability of Mn3O4 nanoparticles. The proper oxidizing ability of Mn3O4@G-A can inhibit the oxidation of SO2 to SO3, thus further avoid the formation of NH4HSO4 and improve the SO2 resistance. Our work here not only solves the current problem of poor SO2 resistance of Mn-based catalysts, but also provides new insights into the design and synthesis of MOF-derived graphitic carbon-containing catalysts for SCR applications.